Vertical I-Joists?

Q.When building a
super-insulated house, one of the ways to increase
insulation levels in the wall assembly is to increase
the thickness of the wall. But instead of using
double-wall framing, would it be okay to frame walls
with I-joists?

A.Gary Schweizer, P.E., a
senior engineer with iLevel by Weyerhaeuser in
Charlotte, N.C., responds: Yes, I-joists can
be used to build walls. You’ll probably
need engineering assistance to help with the
design, since specific application guidelines and
details haven’t been developed by the
I-joist industry or adopted by any building codes.
Tall walls and high-wind or seismic locations will
require engineering to ensure the lateral stability
of the I-joist flanges, which under normal
conditions could be provided by exterior sheathing
and interior drywall. Engineered solutions will be
required when wall framing exceeds certain heights,
too.

You’ll also need to provide full-depth
bottom and top plates to ensure even vertical
loading. Since the majority of compression forces
are distributed to the flanges, a 9½-inch
I-joist will require 9½-inch-wide plates
so that both flanges have full bearing. In
addition, the bottom and top ends of the I-joist
will require web stiffeners or end blocking to help
with vertical load transfer and with the lateral
connections with the plates. Intermediate I-joist
blocking may also be required for fire stopping and
installation stability.